I think this may be related to Bug #129183, which I reported earlier - in that case, I was trying to enable a different wireless card on the same laptop, but with the same result - blank screen.
In any event, for this bug, either it doesn't happen or happens less frequently if I shut down the wireless interface (ifdown ath0) before saving a new /etc/network/interfaces file.
The previous bug involved the built-in ra2500 card, this one has been happening while I was trying to use a Netgear WG511T or WG511TNA card (both designations appear on the box!).
I think this may be related to Bug #129183, which I reported earlier - in that case, I was trying to enable a different wireless card on the same laptop, but with the same result - blank screen.
In any event, for this bug, either it doesn't happen or happens less frequently if I shut down the wireless interface (ifdown ath0) before saving a new /etc/network/ interfaces file.
The previous bug involved the built-in ra2500 card, this one has been happening while I was trying to use a Netgear WG511T or WG511TNA card (both designations appear on the box!).